1. Field
The presently disclosed subject matter relates to semiconductor light-emitting devices including a semiconductor light-emitting chip and to manufacturing methods for the same, and more particularly, to semiconductor light-emitting devices for a vehicle light, for example a headlight, that can provide a favorable horizontal cut-off line for a low beam without a shade, and to methods of manufacturing such devices.
2. Description of the Related Art
Semiconductor light-emitting devices that include an LED chip have been used for vehicle headlights in recent years. Vehicle headlights can be classified into two major groups, a reflector type and a projector type. A conventional LED light source using a plurality of LED chips and a vehicle lamp using the light source, for example, are disclosed in Patent Document No. 1 (U.S. Pat. No. 7,520,647 (commonly assigned)). The conventional LED light source disclosed in Patent Document No. 1 can be used as a light source for a reflector type headlight.
When the conventional LED light source is used for a vehicle headlight, the headlight forms a light distribution pattern by reflecting light emitted from the LED light source by a reflector. When a light distribution pattern for a low beam is formed by the LED light source and the reflector, the vehicle headlight may form the light distribution pattern including a horizontal cut-off line by shielding an upward light that gives a glaring type light to an oncoming vehicle and the like by using a shade.
A semiconductor light-emitting device using a plurality of LED chips can also be used as a light source for a projector type headlight and is disclosed in Patent Document No. 2 (Japanese Patent Application Laid Open JP2009-218274). FIG. 8 is a top view showing the conventional semiconductor light-emitting device disclosed in Patent Document No. 2. FIG. 9 is a cross-section view depicting the conventional semiconductor light-emitting device taken along line B-B shown in FIG. 8, and FIG. 10 is a partial close-up cross-section view depicting a principal portion of the semiconductor light-emitting device of FIG. 9.
The conventional semiconductor light-emitting device 60 includes: a base board 50; semiconductor light-emitting chips 51 mounted on the base board 50; a wavelength converting layer 52 formed around the semiconductor light-emitting chips 51 by a stencil printing method and the like so as to encapsulate the semiconductor light-emitting chips 51 along with the base board 50; a frame 58 located on the base board so as to surround the wavelength converting layer 52 encapsulating the semiconductor light-emitting chips 51; and a reflecting member 54 located between the wavelength converting layer 52 and the frame 58 while tightly contacting with a side surface 53 of the wavelength converting layer 52, and the reflecting member 54 made by mixing a diffusing material such as titanium oxide, aluminum oxide and the like with a transparent resin.
A difference between the semiconductor light-emitting device 60 and the above-described conventional LED light source used for the reflector type headlight relates to the reflecting member 54. The conventional LED light source may not include the reflecting member 54 described later because the shade may shield the upward light that emits a glaring type light to an oncoming vehicle, etc.
When the semiconductor light-emitting device 60 is used as a light source for a vehicle headlight, the vehicle headlight may form a light distribution pattern for a low beam via a projector lens. In this case, a boundary 55 between the wavelength converting layer 52 and the reflecting member 54 may form a horizontal cut-off line in the light distribution pattern for a low beam via the projector lens. Accordingly, the semiconductor light-emitting device 60 is located in the vehicle headlight along with the projector lens so that the side surface 53 of the wavelength converting layer 52 corresponding to the boundary 55 can project the horizontal cut-off line of the light distribution pattern.
However, it may be difficult for the semiconductor light-emitting device 60 to provide the side surface 53 of the wavelength converting layer 52 on the same surface as the boundary 55 between the wavelength converting layer 52 and the reflecting member 54 as shown in FIG. 9. That is because a curved surface 56 and/or a concave-convex surface 57 may exist near the boundary 55 between the wavelength converting layer 52 and the reflecting member 54 due to deformation of the wavelength converting layer 52 which may occur during formation of the wavelength converting layer 52 as shown in FIG. 10.
Therefore, the boundary 55 between the wavelength converting layer 52 and the reflecting member 54 is subject to deformation of the curved surface 56 and/or the concave-convex surface 57 as shown in a close-up view in the circle of FIG. 8. Thus, it is difficult for the reflecting member 54 to maintain a linear e boundary 55 between the wavelength converting layer 52 and the reflecting member 54, which projects the horizontal cut-off line for a low beam via the projector lens.
The reflecting member 54 includes a reflective filler having fluidity due to a low viscosity, and is filled in a space between the wavelength converting layer 52 encapsulating the semiconductor light-emitting chips 51 and the frame 58 located on the base board 50. Accordingly, the reflecting member 54 may be in close contact with the side surface 53 of the wavelength converting layer 52 so as to wholly cover the side surface 53 of the wavelength converting layer 52 therewith.
In this case, when the reflecting member 54 having a low viscosity is injected into the space between the wavelength converting layer 52 and the frame 58 in a developmental state of the deformation at a top edge portion of the wavelength converting layer 52 as described above, the reflecting member 54 that reaches to the top edge portion of the wavelength converting layer 52 may rise on the curved surface 56 and/or the concave-convex surface 57, which is developed at the top edge portion of the wavelength converting layer 52.
The reflecting member 54 that reaches the curved surface 56 and/or the concave-convex surface 57 at the top edge portion of the wavelength converting layer 52 may interrupt light-emission of the semiconductor light-emitting chips 51 from the wavelength converting layer 52 toward the outside of the light emitting device 60, and may cause a reduction of a beam flux of light emitted from the semiconductor light-emitting device 60. Additionally, the reflecting member 54 that reaches the curved surface 56 and/or the concave-convex surface 57 of the wavelength converting layer 52 may cause a reduction of characteristics of the horizontal cut-off line for a low beam because the linear nature of the boundary 55 between the wavelength converting layer 52 and the reflecting member 54 that forms the horizontal cut-off line beam reduces.
The horizontal cut-off line of the light distribution pattern for a low beam is formed by a light blocking effect of the reflecting member 54. The light blocking effect of the reflecting member 54 is due to a feature that diffuses incoming light entering into the reflecting member 54 with the diffusing material such as the titan oxide, etc. The reflecting member 54 has a high reflectivity and diffusibility, however, part of the incoming light entering into the reflecting member 54 may slightly leak as a diffusing light to the outside because of diffusing reflection.
The amount of diffusing light that leaks from the reflecting member 54 to the outside may be determined by a thickness of the reflecting member 54 and a density of the diffusing material in the reflecting member 54. The characteristics of the horizontal cut-off line may be determined by a ratio of a light intensity of light emitted from the wavelength converting layer 52 and a light intensity of the diffusing light leaked from the reflecting member 54 and by a shape of the boundary 55 between the wavelength converting layer 52 and the reflecting member 54.
In this case, the smaller the ratio of the light intensity of the light emitted from the wavelength converting layer 52 and the light intensity of the diffusing light leaked from the reflecting member 54, the sharper the horizontal cut-off line is, because a difference in the light intensity in the boundary 55 between the wavelength converting layer 52 and the reflecting member 54 is large.
When the top edge portion of the wavelength converting layer 52 is curved, because the reflecting member 54 covers the top edge portion of the wavelength converting layer 52 as shown in FIG. 10, the light-emitting region of the wavelength converting layer 52 is reduced. In addition, because a thickness of the reflecting member 54 near the boundary 55 between the wavelength converting layer 52 and the reflecting member 54 becomes thin, the light blocking effect is reduced near the boundary 55. Consequently, the characteristics of the horizontal cut-off line degrade, especially in regard to the linearity of the horizontal cut-off line and a contrast between a top and bottom of the horizontal cut-off line.
When the density of the diffusing material in the reflecting member 54 is high density in order to enhance the light blocking effect of the reflecting member 54, adhesions between the reflecting member 54 and the wavelength converting layer 52 and between the reflecting member 54 and the frame 58 may be reduced because a density of the transparent resin having an adhesivity in the reflecting member 54 is reduced.
Therefore, the density of the diffusing material with respect to the transparent resin should be maintained at an effectual value in order to manufacture the semiconductor light emitting device 60 so as to have high reliability. Moreover, in order to form a favorable horizontal cut-off line, one can form the wavelength converting layer 52 from the top edge portion to a bottom edge portion so that the side surface 53 of the wavelength converting layer 52 becomes substantially perpendicular to the base board 53.
However, in a process for forming the wavelength converting layer 52, it may be difficult to form the side surface 53 of the wavelength converting layer 52 from the top edge portion to the bottom portion in a plane perpendicular to the base board 53. Thus, it may be difficult for the conventional semiconductor light-emitting device 60 to provide a favorable horizontal cut-off line for a low beam.
In the above-described LED light source used for the reflector type headlight, the reflecting member 54 may not be required. However, the reflector and the shade for forming the horizontal cut-off line are required to provide a headlight having a favorable light distribution pattern. Therefore, the reflector type headlight may become large in size as compared with the projector type headlight.
The above-referenced Patent Documents are listed below, and are hereby incorporated with their English abstracts in their entireties.    1. Patent Document No. 1: U.S. Pat. No. 7,520,647    2. Patent Document No. 2: Japanese Patent Application Laid Open JP2009-218274
The disclosed subject matter has been devised to consider the above and other problems, features, and characteristics. Thus, embodiments of the disclosed subject matter can include semiconductor light-emitting devices that can form a favorable horizontal cut-off line for a low beam, and associated manufacturing methods that do not cause and/or are designed to prevent some of the above-described problems, concerns, and characteristics related to a wavelength converting layer. The disclosed subject matter can also include a projector type headlight for a low beam using the semiconductor light-emitting device that can form the favorable horizontal cut-off line without a shade.